Method For Energy Saving In A Telecommunication System

ABSTRACT

The present invention relates to a method for energy saving in a telecommunication system with at least one first base station  24  for enabling communication within a first cell. A signal having a frame structure is transmitted in the first cell by the first base station  24 . The structure of at least some frames comprises an overhead part with at least synchronization or system information. The first base station  24  is in a normal mode operated to transmit at least the overhead part so that it substantially reaches all user terminals within the first cell covering a first area  27 . The method is particularly characterized in that the first base station  24  in a power saving mode is operated to transmit at least the overhead part so that it substantially reaches all user terminals within the first cell covering a second area  23  being larger than the first area  27.

TECHNICAL FIELD

The present invention relates to a method for energy saving in atelecommunication system according to claim 1, a telecommunicationsystem according to claim 14 and a node according to claim 12.

BACKGROUND

Mobile communication is one of the most important technologies forcontributing to social and economic development around the world.Optimizing energy efficiency will not only reduce environmental impact,it will also cut network costs which will give benefits for all usingthe mobile systems.

Capital expenditure typically represents a very small portion of thetotal cost of the ownership. Instead, the long term savings from sitereduction and efficient operation is significant, with a significantreduction in energy consumption as a key issue.

Optimizing solutions for reducing energy consumption means that everystone has to be turned over. Still, the total network solution isgreater than the sum of their parts. This means that combining the bestcomponents in a package does not always give the best results. In theradio base station the relative energy consumption of the differentcomponents vary on the dependency of the properties of the components ithas to work with.

Typical sources of energy consumption in the base station are signalprocessing, RF conversion, power amplification, power supply, climateequipment (air conditioning) and feeder. For instance, In traditionalbase stations the equipment is located on the ground which means thatthe antennas has to be fed using several meters of cable. Half of theemitted power can be lost in the feeders. By placing the equipment inthe top of the tower, significant reductions in energy consumption isachieved. The equipment can be combined with a battery back-up unit thatminimizes hardware and energy consumption.

One way of reducing the energy consumption is to avoid unnecessary DC/DCconversion and reduce the need of cooling fans and cooling systems.Modules based on digital power management can also reduce energyconsumption.

Another way in which energy reduction can be achieved is through the useof stand-by modes. Base station sites are dimensioned to cope with peakhours. In a cell a number of TRX (transmitters) can run at the sametime. Using power management schemes, some TRX can be put in stand-byinstead of running in idling mode during low traffic hours.

Network design is a key issue improving the energy efficiency. In orderto achieve an energy-efficient design a number of issues have to beaddressed from start. At first, the true network needs has to beaddressed. No amount of energy efficiency at the component level canmake up for an inefficiently deigned network. For instance the number ofradio base stations should be optimized for the coverage and qualitythat needs to be achieved.

The exact coverage, capacity and quality have to be considered beforegetting into considerations about individual sites and equipmentspecifications. Moreover, the current and future business environmentneeds has to be considered, considering the possibility to rebuild orexpand sites. Once these factors have been considered the operatorshould begin the network design process, looking into the total cost ofthe ownership and the alternative design options.

The radio base stations use a large amount of energy. The main task ofthe base transceiver station is to enable communication with the user'sterminal being positioned in the cell. The cells are served by radiotransceivers arranged in a base station. These cells are used to coverdifferent areas in order to provide radio coverage over a wider areathat the area of one cell.

FIG. 1 shows the cellular structure in a telecommunication radionetwork. In the lower part of FIG. 1 is a separate cell with a basestation disclosed for clarity reasons. The cells 10,11 overlap 12 toavoid areas without coverage. There are various solutions fordistinguish the signals from different transmitters in the differentbase stations, such a Code Division Multiple Access (CDMA) and FrequencyDivision Multiple Access (FDMA). Handover is used between the cells formoving user terminals.

The smaller cells 10 are used within city centres where there are a lotof buildings which shields the signal and where there are a lot ofusers. With smaller cells more channels are available in a certaingeographical area which enables communication with more users. Thesmaller cells provide radio coverage and additional capacity where thereare high numbers of users. The base station 13 antennas for thesesmaller cells are mounted at street level, typically on the externalwalls of existing structures, lamp posts and other street furniture.Typically, these cells provide radio coverage across smaller distancesand are placed 300 m-1000 m apart. They have an output in the range of afew watts.

The larger cells 11 provide the main coverage in a mobile network. Theantennas for the larger cells are mounted on ground-based masts,rooftops and other existing structures. They must be positioned at aheight that is not obstructed by surrounding buildings and terrain.Large cells base stations have a typical power output of tens of watts.These cells also cover the countryside where there are less obstacle andless users per area unit.

Since the cell covers a geographical area, the transmitting power of thetransceivers is a function of the coverage of the transmitted signalsenabling the communication. An obstacle in the area which shields thetransmitted signals means that the power may have to be increased evenmore to provide the quality of service that the operator aims for.

In addition to the expanding telecommunication network requiring moreand more base stations, there is an increasing need of deliveringwireless technology with broadband capacity for cellular networks. Agood broadband system must fulfil certain criteria, such as high datarate and capacity, low cost per bit, good Quality of Service and greatercoverage. High Speed Packet Access (HSPA) and Mobile WiMAX are examplestwo network access technologies that enable this.

These modern standards have very high capacity in terms of users andthroughput, which requires a large amount of energy. In order to achievehigh data throughput in the cellular systems a dense cell plan has to bedeployed. A base station for modern standards consumes considerableamount of power, typical 65000 kWh per station and year.

For instance mobile WiMAX transmitted via base stations uses ScalableOrthogonal Frequency Division Multiple Access (SOFDMA) with TimeDivision Duplex (TDD). FIG. 2 shows a schematic view of a framestructure for OFDMA (on which SOFDMA is based) when operating in TDDmode. Some WiMAX systems support OFDMA operating in Frequency divisionduplexing (FDD) in which the frame structure differs from TDD in thatthe uplink and downlink frames are transmitted at the same time overdifferent carriers. The frame (Frame N) comprises a downlink subframe15, a following uplink subframe 16, a small guard interval 20 betweenthe downlink and uplink subframe and an end interval 22 between theuplink and the downlink subframe of the next frame.

The downlink subframe 15 in TDD begins with overhead information forinforming the user device about the characteristics of the system. Theoverhead comprises synchronization information 17 or system information18. The overhead is followed by data regions 19 for the downlink datatraffic in the downlink subframe. A guard interval 20 is followed by anuplink subframe 21 with data regions for the uplink data traffic fromthe different user devices. Finally there is the end interval 22followed by the overhead synchronization information 17 of the nextframe.

In WiMAX particularly the overhead begins with a downlink preamble thatis used for physical-layer procedures (cell detection, time andfrequency synchronization). The preamble is followed by a frame controlheader providing frame configuration and system information (modulationand coding maps) to find where and how to decode downlink and uplink.The frame control header and maps are sent for each available dataregion 19, 21.

In order to achieve high data throughput in cellular systems, high ordermodulation, e.g. 64 QAM and high transmit power is used at the basestation. The physical resources in term of subcarriers and time are keptto a minimum to maximize the user data throughput. High performancepower amplifier is needed to keep the signal properties after theamplification. Especially the linearity of the amplification isimportant. This requires a lot of energy which increases the energyconsumption of the base station. Due to these requirements the amplifierefficiency is low and contributes to a large extent the base stationpower consumption.

During low load or no load scenarios the base station still needs totransmit the system and synchronization information 17,18 to serve theattached user terminals and so a new terminal can access the system. Theinformation has to be transmitted with enough power to reach all userterminals within the cell and is therefore transmitted with lowmodulation order and high output power. Due to these transmissions thebase station power consumption is still quite significant.

SUMMARY

The object of the present invention is to increase the energy efficiencyin cellular radio network. The object is solved by means of a method forenergy saving in a telecommunication system according to claim 1, atelecommunication system according to claim 14 and a node according toclaim 12.

The present invention relates to a method for energy saving in atelecommunication system with at least one first base station forenabling communication within a first cell. A signal having a framestructure is transmitted in the first cell by the first base station.The structure of at least some frames comprises an overhead part with atleast synchronization or system information. The first base station isin a normal mode operated to transmit at least the overhead part so thatit substantially reaches all user terminals within the first cellcovering a first area.

The method is particularly characterized in that the first base stationin a power saving mode is operated to transmit at least the overheadpart so that it substantially reaches all user terminals within thefirst cell covering a second area being larger than the first area.

The invention also relates to a node in the telecommunication systemwith at least one first base station for enabling communication within afirst cell. The first base station is adapted to transmit a signalhaving a frame structure in the first cell. The structure of at leastsome frames comprises an overhead part with at least synchronization orsystem information. The first base station is in normal mode operated totransmit at least the overhead part so that it substantially reaches alluser terminals within the first cell covering a first area.

What particularly characterizes the node is that it is adapted tocontrol so that the first base station in the power saving mode isoperated to transmit at least the overhead so that it reaches all userterminals within the first cell covering a second area being larger thanthe first area.

The invention also relates to a telecommunication system with at leastone first base station for enabling communication within a first cell.The first base station is adapted to transmit a signal having a framestructure in the first cell. The structure of at least some framescomprises an overhead part with at least synchronization or systeminformation. The first base station is in normal mode operated totransmit at least the overhead part so that it substantially reaches alluser terminals within the first cell covering a first area.

What particularly characterizes the system is that it is adapted tocontrol so that the first base station in the power saving mode isoperated to transmit at least the overhead so that it reaches all userterminals within the first cell covering a second area being larger thanthe first area.

The advantage of the present invention is that the introduction offlexible cell structure and base station sleep mode, the powerconsumption is drastically decreased. The invention can be introduced inexisting cellular standards without change of the air interfacestandards.

BRIEF DESCRIPTION OF DRAWINGS

In the following text the invention will be described in detail withreference to the attached drawings. These drawings are used forillustration only and do not in any way limit the scope of theinvention:

FIG. 1 shows the cellular structure in a telecommunication radionetwork.

FIG. 2 shows a detailed schematic view for the OFDMA frame structurewhen operating in TDD mode.

FIG. 3 shows the cellular structure in the telecommunication networkaccording to the present invention.

DETAILED DESCRIPTION

The invention will now be described in detail with reference toembodiments described in the detailed description and shown in thedrawings. FIGS. 1 and 2 have already been described in relation toBackground above.

The embodiments refer to a method for energy saving in atelecommunication system. The telecommunication system and node areadapted for performing said method described herein.

The present invention relates to a method for energy saving in atelecommunication system with at least one first base station 24, seeFIG. 3, for enabling communication within a first cell. The first cellsare served by radio transceivers arranged in the base station 24. Thesecells are used to cover different areas in order to provide radiocoverage over a wider area that the area of one cell.

FIG. 1 shows the cellular structure in a telecommunication radionetwork. In the lower part of FIG. 1 is a separate cell with a basestation disclosed for clarity reasons. The cells 10,11 overlap 12 toavoid areas without coverage.

The first base station 24, see FIG. 3, transmits a signal having a framestructure in the first cell. The structure of at least some framescomprises an overhead part with at least synchronization (17) and system(18) information. It is not necessary that all frames contain anoverhead part. For instance in GSM, which is one of thetelecommunication systems in which the present invention can beimplemented, only some of the frames contains an overhead part. In othersystems, such as WiMAX, all frames contain an overhead part.Consequently, a person skilled in the art should realize that alltelecommunication systems are included within the scope of theinvention.

The embodiment shown in FIG. 2, which relates to TDD, comprises asubframe 15 followed by a subframe 16. The frame structure in TDD isdivided into a downlink subframe a following uplink subframe, a smallguard interval 20 (see FIG. 2) between the downlink and uplink subframeand an end interval 22 (see FIG. 2) between the uplink and the downlinksubframe of the next frame. It should however be understood by theperson skilled in the art that the feature subframe also includesembodiments with FDD, in which the subframes are divided by frequencyinstead, or other technologies for duplex.

The first base station 24, see FIG. 3, in normal mode is operated totransmit at least the overhead part so that it substantially reaches alluser terminals within the first cell covering a first area 27. The firstgeographical area is the default area for normal operation.Substantially reaching all user terminals means that there might be userterminals within the cell which from which the transmitted signals areshielded (for instance by a concrete wall). The feature “reaches alluser terminals within the first cell” is used to define the first area.This means that the coverage of the overhead part, which is transmittedwith at least some of the cells, defines the first area.

The object of the present invention is to increase the energy efficiencyin cellular radio network. The scope of the present invention istherefore that the first base station 24, see FIG. 3, in a power savingmode is operated to transmit at least the overhead 17,18 so that itreaches all user terminals within the first cell covering a second area23 being larger than the first area 27. As seen in FIG. 3, three basestations 24 increases the area 27 of the respective cell significantly.Also the second area is defined by the coverage of the overhead part,which is transmitted with at least some of the cells.

The advantage is that the introduction of flexible cell 23,27 structureand power saving sleep mode, the power consumption of the cellularsystem is drastically decreased. The invention can be introduced inexisting cellular standards without change of the air interfacestandards. As will be described the increase of the cell area to asecond, larger area 23 is combined with an interruption of transmittingin other base stations 25.

In normal mode the first base station 24 transmits with a first powerlevel and in the power saving mode transmits with a second power leverbeing higher than the first power level. This is one option how toincrease the area 27 of the cells. Another option is that the first basestation 24 in the normal mode transmits via a first antenna device andin the power saving mode transmits via a second antenna device.Different antennas have different properties, and by using differentantenna devices (they may be combined) a variation in area size isenabled. The fact that the same base station 24 is used for increasingthe cell size means that the second larger area 23 will overlap thefirst area 27.

In order to achieve the power saving on a system level there is at leasta second base station 25 which in a normal mode is operated to transmitat least the overhead so that it substantially reaches all userterminals within a cell covering a third area 26. Also the third area isdefined by the coverage of the overhead part, which is transmitted withat least some of the cells.

By interrupting the transmitting from the second base station in powersaving mode a significant energy saving is achieved. A majority of basestations 25 may be switched off during power saving mode, and the cellswith a third area 26 during the power saving mode is also substantiallyoverlapped by the second area 23. Thereby, as exemplified in FIG. 3, byswitching off 27 out of 30 base stations 25, a significant amount ofenergy will be saved even though these three has to increase their cellarea 23. As can be seen, the second area 23 overlaps areas 26, 27 ofdifferent size which means that base stations serving both smaller andlarger cells can be part of the power saving operation.

As an option the base station 24 may increase or decrease the secondarea 23 in which the first base station transmits at least the overhead.Thereby, if the number of cells increases in the system, the same basestations 24 still serves in power saving mode.

As an option the signal transmitted, having a frame structure, containsan overhead part 17, 18 in each transmitted signal. In GSM some framescontain an overhead part while in other systems such as WiMAX all framescontains an overhead part.

The overhead part needs to be transmitted in order for the user terminalto receive synchronization or system information. If some base stations25 are interrupted, the base stations 24 operating in power saving modemust make sure that at least the overhead 17,18 substantially reachesall user terminals within the second cell 23 substantially overlappingthe third cell 26.

The power saving mode is activated by the system at certain operatingconditions such as the level of usage for the cell capacity, the numberof user terminals in the cell and/or statistics of cell usage over time.The first base station 24 would typically switch between normal mode andpower saving mode by some management commands from a management node.Management commands will also interrupt the operation of the second basestation 25 during the power saving mode. When at least one of the secondbase stations should be awakened from the interruption period during thepower saving mode, management commands are also used. During theinterruption period, the second base station has the capability toreceive some “wake-up” commands, power up and resume normal operation.It may be that only some of the base stations switch to or from powersaving mode. This for instance depends on the power saving setting isthe system, for instance made by the operator.

The intent of the present invention is to monitor the systemcontinuously and if the traffic load goes down for a period of time thepower saving mode may be activated. Using statistics of traffic loadover time will also be very useful. For instance it may be that anoperator has monitored a low traffic load in a certain cell at nightbetween midnight and 06.00 in the morning. The operator may then via amanagement system modify the operation of this base station so that thepower saving mode is activated every night between midnight and 06.00.The system may also be modified so that if the traffic load is below acertain level the power saving mode is activated. It is the operatorthat decides which quality of service that will be provided at certainconditions.

The power saving mode is controlled by an algorithm which is loaded intothe system in order to enable said method for energy saving.

The invention also relates to a node in the telecommunication systemwith at least one first base station 24 for enabling communicationwithin a first cell. The first base station 24 is adapted to transmit asignal having a frame structure in the first cell. The structure of atleast some frames comprises an overhead part with at leastsynchronization 17 or system 18 information. The first base station 24,see FIG. 3, in normal mode is operated to transmit at least the overheadpart 17,18 so that it substantially reaches all user terminals withinthe first cell 10,11 covering a first area 27.

What particularly characterizes the node is that it is adapted tocontrol so that the first base station 24 in the power saving mode isoperated to transmit at least the overhead 17,18 so that it reaches alluser terminals within the first cell covering a second area 23 beinglarger than the first area 27. The node may comprise an algorithm whichcontrols the power saving mode.

The invention also relates to a telecommunication system with at leastone first base station 24 for enabling communication within a firstcell. The first base station 24 is adapted to transmit a signal having aframe structure in the first cell. The structure of at least some framescomprises an overhead part with at least synchronization 17 or system 18information. The first base station 24, see FIG. 3, in normal mode isoperated to transmit at least the overhead part 17,18 so that itsubstantially reaches all user terminals within the first cell 10,11covering a first area 27.

What particularly characterizes the system is that it is adapted tocontrol so that the first base station 24 in the power saving mode isoperated to transmit at least the overhead so that it reaches all userterminals within the first cell covering a second area 23 being largerthan the first area 27. The node may comprise an algorithm whichcontrols the power saving mode.

It will also be appreciated by the person skilled in the art thatvarious modifications may be made to the above-described embodimentswithout departing from the scope of the present invention.

There are no particular demands on the first base stations 24 being ableto switch between “low” power normal mode and “high” power, power savingmode apart from the capability to provide the desired coverage of thesecond area 23.

A variant of the disclosed embodiment is that the first cells 24 duringthe power saving mode to provide a large second area 23 coverageswitches to a more robust coding and modulation scheme.

1. Method for energy saving in a telecommunication system with at leastone first base station for enabling communication within a first cell, asignal having a frame structure being transmitted in the first cell bythe first base station, the structure of at least some frames comprisingan overhead part with at least synchronization or system information,the first base station in a normal mode being operated to transmit atleast the overhead part so that it substantially reaches all userterminals within the first cell covering a first area, the first basestation in a power saving mode being operated to transmit at least theoverhead part so that it substantially reaches all user terminals withinthe first cell covering a second area being larger than the first area.2. The method according to claim 1 wherein the first base station in thenormal mode transmits with a first power level and in the power savingmode transmits with a second power lever being higher than the firstpower level.
 3. The method according to claim 1 wherein the first basestation in the normal mode transmits via a first antenna device and inthe power saving mode transmits via a second antenna device.
 4. Themethod according to claim 1 wherein the second area overlaps the firstarea.
 5. The method according to claim 1 wherein at least a second basestation in a normal mode is operated to transmit at least the overheadpart so that it substantially reaches all user terminals within a secondcell covering a third area, the transmitting from the second basestation in power saving mode being interrupted.
 6. The method accordingto claim 5 wherein the second area during the power saving mode alsosubstantially overlaps at least the third area.
 7. The method accordingto claim 1 wherein the second area overlaps areas of different size. 8.The method according to claim 1 wherein the size of the second area inwhich the first base station transmits at least the overhead, candecrease or increase.
 9. The method according to claim 1 wherein saidoverhead part is contained in each transmitted signal.
 10. The methodaccording to claim 1 wherein the power saving mode is activated atcertain operating conditions such as the level of usage for the cellcapacity, the number of user terminals in the cell and/or statistics ofcell usage over time.
 11. The method according to claim 1 wherein thepower saving mode is controlled by an algorithm.
 12. A node in atelecommunication system with at least one first base station forenabling communication within a first cell, the first base station beingadapted to transmit a signal having a frame structure in the first cell,the structure of at least some frames comprising an overhead part withat least synchronization or system information, the first base stationin a normal mode being operated to transmit at least the overhead partso that it substantially reaches all user terminals within the firstcell covering a first area, the node being adapted to control so thatthe first base station in a power saving mode is operated to transmit atleast the overhead part so that it substantially reaches all userterminals within the first cell covering a second area being larger thanthe first area.
 13. The node according to claim 12 wherein the nodecomprises an algorithm controlling the power saving mode.
 14. Atelecommunication system with at least one first base station forenabling communication within a first cell, the first base station beingadapted to transmit a signal having a frame structure in the first cell,the structure of at least some frames comprising an overhead part withat least synchronization or system information, the first base stationin a normal mode being operated to transmit at least the overhead partso that it substantially reaches all user terminals within the firstcell covering a first area, the system being adapted to control so thatthe first base station in a power saving mode is operated to transmit atleast the overhead part so that it substantially reaches all userterminals within the first cell covering a second area being larger thanthe first area.
 15. The telecommunication system according to claim 14wherein the system comprises an algorithm controlling the power savingmode.